I currently have internet connections from my ethernet port and wired router. These work fine and I don't necessarily want to change them.

However I have a Kindle and would like to have wifi for it. What do I need to do? I'm thinking a usb wifi adapter would work. Then what? Do I need another router? How does it get setup? Can I do it only for the Kindle and maybe my cell phone?

In order to have WiFi, you will need to have a WiFi router. Some routers are both wired ethernet and WiFi. You don't need a USB adapter for your computer if your going to leave it wired. The adapter is for the device; the router is to provide the WiFi signal which the adapter can pick up.

The Kindle doesn't need an adapter - it has built-in WiFi.

Once you have a WiFi signal in your house, any device with WiFi capabilities will be able to pick it up.

So, it depends on what kind of router you have now or if you need to get a new one.

I have a D-Link 4100 DGL. My Kindle currently works off 3G but I may replace it and I would rather simplify with wifi. I may go Fire, I'm not sure yet.

Will my router which is wired also handle wireless?

This whole wireless business is like a snakepit to me. I'm afraid I'm going to get stuck trying to work it out. But First Things First. I need to know what equipment is needed and then what the next step would be.

I have roku, blueray, my pc, Xbox currently hooked up. I don't have a network that I know of.

The DGL 4100 is not a WiFi Router. If you want to go WiFi, you will have to get a WiFi router. The link Winfrey provided is a good comparison to your router. They are very old technology from 2005. The new ones are MUCH more secure and faster to boot.

If you want to stay with D-Link, this is an example of a wireless router that also has 4 ethernet ports for wired connections. So, if that's what you want, you could continue to have all 4 of your devices plugged in to an ethernet port. But if any of them are wireless (WiFi), you might be able to get rid of some ethernet cables.

You can have 4 wired connections on this particular router and as many wireless connections as you have wireless devices. Of course, if you have too many using the internet "pipeline" at the same time, it can bog down the speed depending on what kind of internet service you have.

I assume you have cable or DSL or something like that for your internet service. You plug the cable for the internet service into the port that says Internet (on this router model). That brings the internet to the router. Then you just plug your computer into one of the four ethernet ports. It will pretty much work exactly like the one you have now, except it will also be putting out a WiFi signal. If someone comes to your house with a smart phone, give them your password and they can connect to your WiFi. Get a Kindle Fire and you can connect it to your WiFi. And on like that.

To be honest, you really don't even need to set up a home network unless you have multiple computers that you want to share data between. Just plug in your wired components and set up your wireless components. D-Link or whatever brand you get will pretty much walk you through getting it all set up. Just make sure you set up security preferably using the WPA2 standard. Again, this will all be specified for the wireless router you buy.